Disk brake calliper

ABSTRACT

In order to obtain a brake caliper for a disk brake which is light and at the same time resistant to bending, the caliper is manufactured from a metal-matrix composite material having embedded ceramic particles. In order not to have to carry out the necessary subsequent machining steps in the hard composite material, it is provided according to the invention that, at least in the area of the brake cylinder and the supply connection, the caliper housing is provided with one or several inserts made of an easy to machine material, preferably an aluminum alloy.

BACKGROUND OF THE INVENTION

The invention involves a caliper for disk brakes according to thepreamble of claim 1.

Higher and higher demands are being placed on the performance of moderndisk brakes. Thus the brake itself and especially the caliper housingshould be light on the one hand, in order to minimize the unsprungweight on the vehicle wheel while on the other hand, the caliper must bevery rigid so that it does not bend very much under large stress.

The use of aluminum alloys for the brake caliper, instead of theconventional iron workpieces, is increasing in order to save weight.Aluminum alloys have the disadvantage, however, that their strengthdecreases for temperatures above 300° C. Such temperatures can certainlyoccur for disk brakes in extreme cases. To solve this problem materialsare suitable which are known as metal-matrix composite materials. Theseinvolve composite materials made of metal and ceramic particles orfibers of varying lengths. In order to cast brake calipers, a compositematerial of aluminum and ceramic particles is especially suitable, forexample particles of silicon carbide.

Such a metal-matrix composite material with ceramic particles isconsiderably less flexible than aluminum alloys. It allows theconstruction of lightweight brakes which are considerably reduced inconstruction space as opposed to brakes made of aluminum andnevertheless have a high rigidity. A disadvantage of this compositematerial is its high hardness which is attributable to the ceramicparticles. A rough-cast caliper housing is thus very difficult tosubsequently machine, in order, for example, to put in threading for thehydraulic fluid supply connection or a gasket ring groove in the brakecylinder. The processing is laborious, expensive and only possible usingdiamond tools, unless one is willing to put up with minimal service lifefor the tools. Subsequent machining is thus out of the question foreconomic reasons.

For the casting of metal-matrix composite materials, the known"lost-foam-process" is available. In this process, a high-resistancefoam core of the caliper housing is manufactured which is embedded in acasting mold in sand and then cast using the metal-matrix compositematerial. It is possible to cast undercuts using this process so thatthe unfinished part does not have to be subsequently machined, at leastas far as the undercuts are concerned. In this process, severalsubsequent machining steps are already saved. At other positions, asubsequent machining is necessary in spite of this, especially if verysmall tolerances are necessary, which cannot be achieved in the mold.This is regularly the case for threaded connections, piston bore holes,grooves or recesses.

SUMMARY OF THE INVENTION

The purpose of the invention is to create a brake caliper which consistsof a metal-matrix composite material and for which designs having narrowtolerances such as threaded connections, piston bore holes or groovescan be manufactured economically.

The solution for this purpose results from the characterizing part ofclaim 1. In principle, the solution consists in forming the positions ofthe caliper provided for an exact subsequent machining from a softer andeasier to process material, in particular an aluminum alloy. Putting inthe easier to process material occurs, in a first embodiment accordingto the process claim 8, in the form of insert pieces which are embeddedin the high-resistance foam core of the caliper housing, are cast inusing the metal-matrix composite material during casting, and then enterinto a tight connection with this material. After that the resultingunfinished part can be completed by machining the insert pieces.

Insert pieces are particularly used in the brake cylinder and at thesupply connection for the hydraulic fluid. It is functional to alsoprovide an insert piece for a bleeder opening. In a refinement of theinvention, the tight connection between the insert pieces and themetal-matrix composite material is further improved by providing theinsert piece with a denticulation or fluting.

In a second embodiment of the invention, the insert pieces are not castin. In this case, the caliper housing is manufactured according to theprocess described in claim 9. Here an unfinished housing piece is firstmanufactured from metal-matrix composite material. The insert pieces arecast separately, finished, and afterwards inserted into the unfinishedhousing piece. In a preferred embodiment, a single combined insertpiece, which is inserted into the precision-cast cylinder opening, issufficient for the brake cylinder and the hydraulic connection. In thisway, the combined insert piece can be mounted by being pressed into itsinstalled position, or it can be secured by a bolt at the supplyconnection and connected to the unfinished housing piece.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiment examples of the invention are explained more closely in thefollowing using the drawings:

Shown are:

FIG. 1 a section through a high-resistance foam core having an insertpiece in the brake cylinder, having the same shape as a rough-castcaliper prior to subsequent machining;

FIG. 2 a partial representation of the rough casting of FIG. 1 inanother sectional plane;

FIG. 3 the rough caliper of FIG. 1 after performance of the subsequentmachining;

FIG. 4 a representation like FIG. 2 after performance of the subsequentmachining;

FIG. 5 a second embodiment example of the invention having a single,fluted insert piece in a representation corresponding to FIG. 2;

FIG. 6 the embodiment example of FIG. 5 after performance of thesubsequent machining;

FIG. 7 embodiment of the invention using a finished and bolted-in insertpiece, in a representation corresponding to FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

In the figures, a brake caliper for disk brakes is seen, having acaliper housing 1, which has a hydraulic brake cylinder 2 and a supplyconnection 3 for the supply of hydraulic fluid. The caliper housing 1 isessentially made up of a metal-matrix composite material based onaluminum with ceramic particles.

In a first embodiment of the invention, the brake cylinder 2 is providedwith a first insert piece 4 and the supply connection 3 is provided witha second insert piece 5 made of an aluminum alloy. The insert pieces 4,5are softer than the metal-matrix composite material and thus also easyto machine using normal tools.

The manufacture of the caliper housing 1 is done "lost-foam casting."There a high-resistance foam core is manufactured first in the shape ofthe caliper housing 1 and provided with the insert pieces 4,5. Becauseof the similarity of shape between the high-resistance foam core and thecaliper housing 1, FIG. 1 can also be viewed as a representation of thehigh-resistance foam core. The high-resistance foam core is thenembedded in a casting mold in sand and cast using metal-matrix compositematerial, such that the high-resistance foam core is burned up and theinsert pieces 4,5 are cast in by the composite material and enter into atight connection with it. The resulting unfinished piece of the caliperhousing 1 is as according to the illustrations of FIGS. 1 and 2. Thenthe unfinished piece is finished by subsequent machining of the insertpieces 4,5. In this process, as shown in FIG. 4, a channel 6 and athreading 7 for the supply connection 3 are put into the insert piece 5.For the insert piece 4, a gasket ring groove 8 and a groove 9 for aprotective cap are put in, based on the representation of FIG. 3, andthe cylinder bore 10 is subsequently machined.

In a variation of the invention, only one insert piece 11, constructedas a single piece and equipped with fluting 12 on its outside walls foran improved form-fit, is provided for the supply connection 3 and thebrake cylinder 2. The subsequent machining is done in the same manner asfor the first embodiment by putting a channel 6 and a threading 7 intothe supply connection 3 (FIG. 6) and by subsequently machining thecylinder bore 10 and the gasket ring groove 8 as well as the protectivecap groove 9, not shown in FIG. 6.

A second embodiment of the invention is represented in FIG. 7. Here, amodified insert piece 13 is used which is designed as a single piece andis for combined use in the brake cylinder 2 and in the hydraulicconnection 3. The insert piece 13 is not cast in, however. Instead, inmanufacturing the caliper housing 1, an unfinished piece is thenmanufactured using "lost-foam-casting," which consists, however, only ofthe metal-matrix composite material. The insert piece 13 is castseparately out of an aluminum alloy and finished, such that the channel6, the threading 7, the cylinder bore 10, the gasket ring groove 8 andthe protective cap groove 9 are put into it. The finished insert piece13 is then inserted into the unfinished housing piece and tightly boltedand secured to the caliper housing 1 with a threaded connection screwingon nut 14.

The invention can, of course, also be advantageously extended for themanufacture and design of a brake mount, with which the brake caliper isattached on the stub axle of the vehicle and is guided in an axiallymovable way.

We claim:
 1. Brake caliper for disk brakes, having a caliper housing, which has a hydraulic brake cylinder and a supply connection for hydraulic fluid, characterized in that the caliper housing is essentially made up of a metal-matrix composite material and, at the least, the brake cylinder and the supply connection are provided with one or more insert pieces made of easily machinable material wherein a combined insert piece for the brake cylinder and the supply connection is inserted or pressed into the cast cylinder opening.
 2. Brake caliper according to claim 1, characterized in that the insert pieces are made of aluminum or an aluminum alloy with an elevated melting point.
 3. Brake caliper according to claim 1, characterized in that the insert pieces are cast.
 4. Brake caliper according to claim 1, characterized in that an insert is provided for a bleeder opening.
 5. Brake caliper according to claim 1, characterized in that the insert pieces are provided with a denticulation or fluting.
 6. Brake caliper according to claim 1, characterized in that the combined insert piece is secured by a threaded connection to the supply connection and is connected to the caliper housing. 